RFID transponders must be tested in their production process in order to detect and mark deficient ones. Deficiency can be detected by measuring their performance through frequency response, which reveals their sensitivity and transponder RF-bandwidth, for example. There exists a performance test standard ISO 18046-3, which is commonly used.
In the case of transponders intended to be used in a far field (radiative field, in contrast to near/reactive field transponders, such as inductive transponders), a problem arises relating to the closeness of individual transponders with each other in typical production lines (e.g. roll to roll production). Far field cannot be easily focused to an individual transponder so that the frequency response would be obtained only from that particular transponder. Thus, on-line performance testing must be made using some indirect route.
Various solutions for this have been presented, such as selecting the transponder to be measured on the basis of its memory content and screening the surrounding transponders or inactivating them for the duration of the far field detection. However these solutions have their own practical problems. A screening structure should be designed separately for each type of transponder, with the consequent additional engineering work.
There are many publications relating to quality control of RFID transponders, patent (application) publications dealing with the present subject in general as well as proposing specific testing solutions are at least EP 1990784, EP 1989559, and CN 10103361, US 2006/0012387, US 2006/271328, US 2006/226983, and WO 2011/042603. In addition, some special devices for testing have been proposed, for example that disclosed in WO 2006/030060. The device comprises a partitioned measuring chamber and capacitive electrodes in each compartment. The device is intended for measuring the excitation signal coupling to and passing through the transponder from one electrode to another. Thus, the device is not as such suitable for real performance testing including frequency response testing.
General problems relating to existing on-line testing technology are inaccuracy, complexity and slowness. Indeed, it has shown to be very difficult to achieve an on-line testing system, which reflects the true performance of the tags with a reasonable instrumentation costs and without restricting the production speed of the transponders. Since the present production technology is very developed, the testing stage is often the stage restricting the speed of the overall process. The present testing methods also vary a lot in their robustness, i.e., their ability to detect faulty transponders if the measurement conditions are slightly changed. For example, some methods are very sensitive to the exact position of the transponder to be tested with respect to the surrounding instrumentation.
Thus, there exists a need for improved RFID testing solutions.